On 2022-01-12 16:03, Martin Frb via fpc-devel wrote:
On 12/01/2022 13:55, Tomas Hajny via fpc-devel wrote:
- The problem is *NOT* a native 64 bit "ppcx64.exe" ?
=> 64 bit compiled targets don't require "extended" from the ppc,
as they themself wont have support for it?
Wrong - applies only to the Win64 target, whereas e.g. 64-bit Linux
(supported by the same compiler targetting 64-bit code) supports
extended. This means that compiling source code with this compiler may
result in a different binary as soon as there's e.g. an extended
contstant included in the source code, or any compile-time
calculations in this precision need to be performed.
Ok, I was too unspecific, I indeed just meant a 64-bit Window
ppcx64.exe to compile a 64 bit target Windows app.
But indeed, I did not think about compile-time evaluations.
Those will indeed differ.
Leaving the question if it is in that case actually desired that they
are done in "extended" precision.
Imagine some code (targeted at Win-64) that uses "extended" (which
will at runtime become "double"? Or at least be less precise than
"extended").
Now if that code, does some calculations with those values, and the
code is written so the calculations happen at runtime => then the
calculations are done at lower precision.
This would potentially affect the result. I guess that would be
expected behaviour.
But, if any change to the code (not even necessarily a functional
change) would allow the compiler to do those calculations at compile
time, then the value changes. And the entire behaviour of the app may
change.
Possible, this could even be a change just in optimization settings
(or upgrading FPC), allowing the compiler to to propagate constants...
So does that mean, any code (that is to be compiled for Win-64bit) is
considered "unstable" if it contains "extended" ?
Not necessarily - when targetting Win64, the user needs to be prepared
for the lower precision. However, imagine that that the user compiles
his source code for target x86_64-linux. The resulting binary and its
output will be exactly the same if the source code is compiled (with the
same options, etc.) on Linux or if it is compiled on Windows using a
Win32 hosted compiler, but it will differ if using a Win64 hosted
compiler. From compiler support point of view, this is an issue.
Tomas
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